As shown in FIGS. 2 and 3, a pair of main surfaces 38 and 39 extending perpendicular to a direction of movement and parallel to each other are provided on front and rear sides of a metal element 32 in the direction of movement, and a slope 41 is formed radially inside the main surface 38 on the front side in the direction of movement so as to be continuous with the latter. A pair of adjacent ones of the metal elements 32 can be pitched relative to each other around a rocking edge 40 extending between the main surface 38 and the slope 41. Therefore, as shown in FIG. 4, when the metal elements 32 are moved from a drive pulley 6 to a driven pulley 11, the main surfaces 38 and 39 of the adjacent ones of the metal elements 32 are placed in abutment against each other to transmit a driving force. When the metal elements 32 are in a state wound around the drive pulley 6 or the driven pulley 11, the interference of the metal elements 32 with each other can be avoided by the pitching around the rocking edge 40.
The metal elements 32 of the belt for the continuously variable transmission perform a rectilinear translating movement in a chord portion of the belt between the drive pulley 6 and the driven pulley 11 and hence, the moving speeds of various portions of the metal element 32 are the same as one another. However, in a state in which the metal elements 32 are wound around the drive pulley 6 and the driven pulley 11, the metal elements 32 perform a rotating movement about rotational axes of the drive pulley 6 and the driven pulley 11 and hence, the moving speed of a radially outer portion of the metal element 32 is larger than that of a radially inner portion of the metal element 32.
At this time, the metal elements 32 wound around the pulleys 6 and 11 are brought into abutment against each other at the rocking edge 40. Therefore, the speed of the rocking edge 40 of each of the metal elements 32 wound around the pulleys 6 and 11 (the pitch circular speed) is equal to the speed of the various portions of the metal elements 32 performing the rectilinear translating movement in the chord portion. Namely, the speed of the rocking edge 40 of the metal elements 32 at belt portions wound around the pulleys 6 and 11 and the speed of the rocking edge 40 of the metal elements 32 at belt portions which are not wound around the pulleys 6 and 11 (i.e., the chord portion), are the same as each other. Therefore, in the state in which the metal elements 32 are wound around the pulleys 6 and 11, the speed of the radially outer portion of the metal element 32 than the rocking edge 40 is larger than the speed of the rocking edge 40, and the speed of the radially inner portion of the metal element 32 than the rocking edge 40 is smaller than the speed of the rocking edge 40.
Now, when the metal elements 32 lie in the chord portion between the drive pulley 6 and the driven pulley 11 to transmit the driving force, the main surfaces 38 and 39 of adjacent ones of the metal elements 32 are brought into close contact with each other and thus are prevented from being inclined. However, when the metal elements 32 lie in the chord portion between the driven pulley 11 and the drive pulley 6 to transmit no driving force, a small gap is produced between the adjacent ones of the metal elements 32 and hence, in a portion A in FIG. 4, the metal elements 32 may be meshed with the drive pulley 6 while remaining inclined in the direction of movement (with the pitching remaining occurred) in some cases. If the metal elements 32 are meshed with the drive pulley 6 while remaining inclined in the direction of movement, a movement for dissolving the pitching of the metal elements 32 and compacting the gap between the metal elements occurs in the chord portion near an outlet of the drive pulley 6 for resisting against an urging force acting between the elements and hence, the following problems arise: the wearing of the metal elements 32 and the pulley 6 is increased, and the power transmitting efficiency is reduced.
Therefore, a belt for a continuously variable transmission described in Japanese Patent Application Laid-open No.2-225840 is designed so that the center of gravity G of the metal element 32 is located in the vicinity of the rocking edge 40 or radially outside the rocking edge 40, thereby preventing a gap from being produced between the metal elements 32 in the chord portion between the driven pulley 11 and the drive pulley 6, so that the metal elements 32 in close contact with one another are smoothly meshed with the drive pulley 6.
More specifically, the speed of the center of gravity G of the metal elements 32 in the chord portion between the pulleys 6 and 11 is equal to the pitch circular speed, but the speed of the center of gravity G of the metal elements 32 wound around the pulleys 6 and 11 is larger than the pitch circular speed, if the center of gravity G lies radially outside the rocking edge 40. In other words, the kinetic energy of the metal elements 32 leaving the driven pulley 11 is larger than the kinetic energy of the metal elements 32 lying in the chord portion. The metal elements 32 lying in the chord portion are urged forwards (toward the drive pulley 6) by a difference between the kinetic energies and are smoothly meshed with the drive pulley 6 in a state placed in close contact with one another.
In the prior art described above, the center of gravity G of the metal element 32 is allowed to lie radially inside the rocking edge 40 even at a distance of 0.5 mm from the latter. However, if the center of gravity G lies radially inside the rocking edge 40, the kinetic energy of the metal element 32 leaving the driven pulley 11 becomes smaller than that of a metal element 32 lying in the chord portion and hence, the metal elements 32 lying in the chord portion cannot be meshed with the drive pulley 6 without being pitched in a state placed in close contact with one another. Therefore, it is required that the center of gravity G of the metal element 32 should lie radially outside the rocking edge 40. In other words, it is required that a relation Vr&lt;Vg should be established when Vr represents a speed of the rocking edge 40 at an instant when the metal element 32 leaves the driven pulley 11, and Vg represents a speed of the center of gravity G of the metal element 32.
Additionally, if the center of gravity G of the metal element 32 moves radially outside too away from the rocking edge 40, the kinetic energy of the metal elements 32 which have left the driven pulley 11 becomes excessive and the metal elements 32 rotate so as to fall forwards, as shown in FIG. 10. As a result, the energy is expended by the interference between a metal ring assembly 31 and a lower portion of an ear portion 36, or by the interference of coupling, thereby resulting in loss of a force for delivering the metal elements 32 forwards. Therefore, there is a possibility that the metal elements 32 could not be meshed with the drive pulley 6 in the state free of the pitching.